1. Field of the Invention
The present invention relates to solar energy collection devices, particularly those employing flat plates which transfer their heat to liquid flowing thereon.
2. The Prior Art
U.S. Pat. No. 3,145,707 discloses the use of corrugated roofing sheets which are blackened on their upper surface and enclosed beneath a glass plate. Water is trickled over the top of the roofing sheets to collect heat absorbed therein. Such arrangement is deficient in that the water vaporizes upon heating and often condenses on the glass which is at a lower temperature thereby blocking and dispersing the sunlight and decreasing the efficiency of thermal energy collection. Further, water running over the top surface of the sheet material removes or erodes the blackened surface, thereby contaminating the carrier media and further reducing the efficiency of the entire system. The choice of blackening agents usable is also limited, many blackening agents in commmon use are so subject to both erosion by and dissolution in the heat transfer liquid that they cannot be economically or effectively used. Other constructions such as those employing tubes to enclose the liquid are unduly expensive and consumptive of materials. An internal-flow steel-sandwich collector described in the December, 1975, issue of "Popular Science", avoids a heat-transfer problem of the U.S. Pat. No. 3,145,707 from the ridges to the valleys, but adds expense in providing a second sheet of metal to achieve the internal flow.